Vacuum pump



1932- K. c. D. HICKMAN 1,857,506

' I VACUUM PUMP. r

Filed Feb. 19, 1929 4 sheets-sheet 1 INVENTOR KENNETH C. D. H/CKMAN ATTORN EY VACUUM PUMP Filed Feb. l9, 1929 4 Sheets-Sheet 2 fiackins 2 INVENTOR KENNETH C. D. HICKMAN ATTO N EY y 1932. K. c. D. HlKMAN 1,857,506

- VAQUUM 1 =fUMP 7 Filed Feb. 19; 1929 4 Sheets-Sheet s 49 Backing z Puvv lp INVENTOR KENNETH D. H/C'K/IAN 25- 6 BY I ATTORNEY May 10, 1932.

K. C. D. HICKMAN' VACUUM PUMP Filed Feb. 19. 1929 4 Sheets-Sheet 4 Backing INVENTOR KENN TH c. 0. H/CKMAN ATTORN EY Patented May 10, 1932 UNITED, STATES PATENT OFFICE KENNETH C. D. EIOKMAN, OF ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, .A CORPORATION OF NEW YORK vacuum rum? Application filed February 19, 1929. Serial No. 341,105.

tainer walls and gather together in droplets or globules. Consequently when mercury atoms forming a stream of the monatomic mercury vapor impinge on cooled glass surfaces or other walls, those atoms hitting mercury globules will inevitably condense while those colliding with glass or other material often suffer reflection. This has the effect that the total area of a condenser presented to mercury vapor is not effective in inducing condensation. Furthermore, mercury has .another disadvantage in pumps of this type, in that gases carried forward by the vapor stream may leak backwards in between the mentioned globules rendering the pressure on the high vacuum side of a pump a definite function of that on the lower side instead of letting it be, within limits, entirely independent thereof. Mercury has the further disadvantage that its vapor pressure at room tem: perature is comparatively high, and may be nearly a micron, so that it becomes necessary to interpose a liquid air trap or other low temperature trap to prevent diflusion of vapor from the pump to the apparatus, on those occasions where high vacua are required. In addition to these disadvantages mercury is poisonous and when spilled, as inevitably happensv in use, scatters widely as droplets that find their way into cracks and crevices in the floors and benches where they produce an unhealthy atmosphere for a rel- W15 atively long period.

In accordance with one feature of the present invention it 1 is proposed to substitute a material for mercury in vacuum pumps which obviates these difliculties and which possesses all of the following especially desirable charit is sufliciently, chemically unreactive not to attack the material of which the pump is made or otherwise react with the commoner gases which are to be evacuated.

Another feature of this invention includes the use of certain difiicultly volatile organic liquids to replace mercury in high vacuum pumps.

An additionalfeature of the invention is the use, instead .of mercury, of certain substituted aromatic esters, notably those of the phthalic acids and in particular normal-dibutyl phthalate.

A further feature of this invention isthe novel pump design, in which the efliciency of operation is improved and the presence of a retarding, collateral stream of actuating vapor is prevented or made unobjectionable.

These features and others will appear from the detailed description and the claims when taken with the drawings, wherein Fig. 1 shows a common type of condensation pump, suitable for employing an organic liquid of my invention as an actuating agent; Fig. 2 shows another type of well-known condensation pump in which an organic liquid may be used as the evacuating agent; Figs. 3, 4 and 5 show improved designs of high vacuum pumps, according to my invention, in which mercury or an organic actuating vapor may be used; Figs. 6 and 7 show details of radiatorstructure whereby heat may be dissipated from the improved pumps without the use of a water jacket.

I have discovered that the numerous" discondensation pumps in place of mercury;'

while many organic liquids heated in con densation pumps yield a good vacuum certain of them are especially satisfactoryfor commercial use. Although low vapor pressure must be a guide to selection, not every' high boiling organic liquid is serviceable, only those which boil-without sensible decomposition are useful. Thus the hlgher paraflins, the long chain aliphatic acids anddently on account of cracking into volatile constituents, thereforce the pump has the double duty of removing gas from the chamber to be exhausted and in removing its own waste products. From my research, I have found that certain substituted aromatic esters, notably those of phthalic acids and in particular normal-dibutyl phthalate have sufiiciently low vapor pressure at room temperature for use Without a liquid air trap and have the added property of increasing the effective speed of exhaustion. Since the vapor of these liquids is molecular rather than monatomic, it has a natural tendency to condense without the necessity. for liquid nuclei whenever the fall of temperature of the vapor stream warrants. These liquids will wet glass so that a cooled glass surface is effective over its whole area in inducing condensation, consequently a very short. compact pump may be used with butyl p'hthalate. The vapor condenses as a film within a well defined zone above which there is little straying. This is in sharp contrast with the behavior of mercury which wanders out of the pump and is to be found deposited at corners and, bends in the adjoining apparatus, and for this reason in former'vacuum pumps of this type the condensing system has of necessity been of relatively great length to lessen the quantity of mercury vapor reach-.

ing the vessel to be evacuated. It should be emphasized at this point that the more suitable organic liquids can be used satisfactorily in existing condensation pumps with no change other than increasing the heat input and/or improving heat insulation or lagging.

One existing type of pump adapted for use with the evacuating a ent of the present invention is shown in Fig. 1 and includes a bulb 10, containing the evacuating liquid 11.

placed above an electric heater designated 12, which generates a stream of evacuating vapor that passes at relatively high velocity through the gooseneck jet 13. The walls of the bulb and the major part of the gooseneck jet may be covered with heat insulating or lagging material 14, which may include an electric heating element, while the free end of this jet is surrounded by a water jacket 15, having an intake for water at 16, and an outlet at 17, so that the vapor is condensed within the area of the water jacket and returned by way of the return tube 18. The inside of the water jacket 15 is formed of a mercury in this type of pump, 0

tube 19 spaced a short distance away from ing through a liquid air trap 20 and a sec ond tube 21 to the chamber or vessel to be evacuated. Where an organic liquid, according to my invention is substituted for the apparatus may be unchanged except r the possible omission of the liquid air trap 20 and-the provision of higher heat input and improved lagging. Under certain conditions, however, it may be desirable to apply a refrigerant such as ice water in the water jacket.

When mercury is employed as the actuating agent its vapor condenses into globules iii-- pressure on the high vacuum side of the backing pump 22, a definite function of that on the low side, instead of allowing it to'remain entirely independentthereof. At the same time, since mercury may have a vapor pressure of nearly a micron at room temperature,

it is necessary'to interpose a liquid air trap 20 or other trap to prevent difltusion of mercury vapor from the pump to the apparatus, on those occasions when the highest vacua are required. It will also be noted that the inner wall 19 of the water jacket becomes heated so that the droplets 24 of mercury have a tendency to be re-evaporated with cer tain of the reevaporated vapor moving outward through tube 19 toward the chamber to be evacuated. 7

My improved liquid may also be used in the commercial type of pump shown in Fig. 2 which includes a container 25 containing a liquid 26 to be heated to form a vapor which passes through a jet 27. An enlarged bulb 28 surrounding the jet 27 is connected with the container 25 to form an annular space which communicates with the tube 29ithat in turn passes through the liquid air trap 30 into the tube 31 leading to the vessel or chamber to be evacuated. The bulb 28 beyond the outlet of jet 27 is constricted into a portion 29 surrounded by a water jacket 30 provided with an intake 31 for the water supply and an outlet 32. The tube 29 leads to any well known backing'pump 33, which may be a mechanical pump, and thence into the atmosphere.

In the operation of this pump the liquid 26 is heated in any well-known manner to de velop a vapor stream passing through-jet 27 into tube 29 and since the annular space about the jet 27 communicates through the tube 29 with the chamber to be evacuated, the stream of vapor entraps the air or gas from this tube and carries it into tube 29. The

vapor'is cooled in the portion of tube 29 surrounded by the water jacket 30" whereupon;

efiiciency and speed of evacuation. InFigs.

3, 4, and 5 I have shown improved pump designs in which either mercury or an organic liquid may be used as the actuating agent, however, I prefer to use an organic liquid, but the invention is not so limited.

Referring to Fig. 3 there is shown a ves-- sel 40 containing a liquid 41 which is to be boiled by any suitable source of heat applied thereto. The vessel 40 is constricted into a jet 42 connected with a reentrant bulb 43 which is distorted into an exaggerated alembicand which is connected to the condensing tube 44 communicating with the vessel to be evacuated through tube 47.

The condensing tube is surrounded by a heat radiator 45 which may be in the form of a metal collar provided with metal radiating fins engaging this tube as shown in Fig. 8.

.By this construction the radiator is formed of one mass of conducting material so that heat liberated at the base may be dissipated throughout the entire area. provide a second heat radiator 46 preferably formedof many separate elements frictional-.

.ly held-around the bulb 43 so that liquid passing it travels to progressively cooler regions; The tube 47 is surrounded by a heat radiator 48in the form of spaced turns of wire twisted into loops as shown in detail in Fig. 7. This radiator 48 is in effect composed of many separate elements so that gas passing them travels to progressively cooler areas. This arrangement thus serves to prevent any of the actuating vapor from passing into the chamberin opposition to the stream of gas to be evacuated. These radiators may all he of sheet metal or all may be of twisted wire or combinations of the two as will be further pointed out. However, I believe it to be novel to provide separate heat dissipating devices at various critical areas on a vacuum pump, each of these heat dissipating devices being independent of each other and operating at a temperature appropriate to its own position. I have found that this last mentioned pump starts evacuating when it is sup ported by only a medium backing or auxilare in intimate contact with each other whereiary pump.

It should.

fined by the bulb 43 is at a considerable dis- In addition I be particularly noted that the inner surface of the annular chamber detance from the wall of the jet 42 and the spacebetween these elements may be packed with heat insulating material or lagging 51 to prevent the transfer of heat from the jet to said chamber. The tube'44 leads to a backing .pump 49 and thence to the atmosphere.

In operation, when liquid 41 boils, it gentube-44. As it does so it entraps the air or gas to be exhausted which is present in the crates a stream of vapor which passes out through the jet 42 at high velocity into the bulb 43. When the vapor reaches the tube 44,

it condenses as a film and drops back into the bulb 43 where it collects as condensate and passes through the return tube 50 into the container 40. As the condensate of the vapor drops down from the tube 44 at relatively high temperature, it must be cooled otherwisethe jet will do most of its work in removing the organic vapor rather than the gas to be exhausted. While the cooling may best be accomplished by a water jacket, I find it much Q turned through the opening 34 into the bulb 25 so that the heat from the wall of the jet 27 causes the condensed vapor, indicated at 36, to move upward as a collateral vapor stream which tends toenter the tube 29 in opposition to the flow of gas. Inv my arrangement, by the separation of the wall of the jet from the inner wall of the bulb 43 this tendency is obviated and the efficiency of the ump materially increased.

Amodified form of the pump, shown in Fig. 4, has the same elements as shown in the pump of Fig.3. In this design, however, the jet 42 is smaller than the condensing tube 44 and projects beyond thew-all of the bulb 43 into the condensing tube. In this pump the radia-. tors 45-, 46'and 48-are all of sheet metal construction, the radiators 46 and 48 being com posed of radiating discs similar to that shown in Fig. 6, frictionally engaging the surfaces which they aredesigned to cool. This par ticular type of pump is especially adapted for operating efficiently with the highest possible backing pressure, that is with a very poor backing or auxiliary pump.

The modified form of pump shown in Fig. 5 likewise has the same number of elements in that the diameter of the jet 42 is the same as the diameter of the tube 44. In this modification the radiators 45, 46 and 48 are shown as made of wire wrapped and formed with projecting loops around the surface to be cooled. The turns-of wire in the radiator 45 diator operates ata temperature eculiar'to its position and independently o the other associated turns.

This type of pump is adapted for high speeds of exhaustion when operating with a good backing pump.

It is obvious that numerous other embodiments of my invention are possible and I contemplate as within my invention all such modifications and equivalents as fall Within the scope of the appended claims.

WVhat I claim is:

1. A vacuum pump comprising means for producing a stream of vapor, a condensing tube, a jet through which said stream of vapor flows to said condensing tube, a bulb connecting said jet and said tube, a conduit communicating with the receptacle to be exhausted and with said bulb, and separate heat dissipating means for the condensing tube and for the bulb.

2. A'vacuum pump comprising means for producing a stream of vapor, a condensing tube, a jet through which the stream of vapor flows to the condensing tube, a bulb connecting said jet with said tube, a conduit communicating with the receptacle to be exhausted and with said bulb,and separate heat dissipating means for the condensing tube, for the bulb and for the conduit.

3. A vacuum pump comprising a liquid container terminating in a jet, liquid in said container, means for heating said liquid, a condensing tube, a bulb connecting said jet and said condensing tube, said bulb forming an annular chamber widely separated from the wall of said jet, a separate heat radiator for said bulb, a conduit communicating with said annular chamber and leading to a receptacle to be evacuated, and a return tube tube, a jet through which the stream of vapor flows upward to the condensing tube, a bulb which is a continuation of the lower end of said condensing tube, a conduit attached to the bulb and communicating with the receptacle to be exhausted and with said bulb, and separate metallic projections adapted for air cooling attached in heat exchange relation to the condensing tube and to the bulb respectively.

5. Avacuum pump comprising means for producing a stream of vapor, a condensing tube, a jet through which the stream of vapor flows upward to the condensing tube, a bulb which is a continuation of the lower end of. said condensing tube, a conduit attached to the bulb and communicating with the receptacle to be exhausted and with said bulb, and separate metallic projections adapted for air cooling attached in heat exchange relation to the condensing tube, to the bulb and to the conduit respectively.

6. A vacuum pump comprising means for producing a stream of vapor, a condensing tube, a jet through which the stream of vapor flows upward to the condensing tube, a bulb which is a continuation of the lower end of said condensing tube, and insulating means surrounding said jet adapted to substantially prevent transfer of heat from the jet to the bulb and a conduit communicating with the receptacle to be exhausted and the said bulb, and separate metallic projections adapted for air-cooling attached in heat exchange relation to the condensing tube and to the bulb respectively.

7. A vacuum pump comprising means for producing a stream of vapor, a condensing tube, a jet through which the stream of vapor flows upward to the condensing tube, a bulb which is a continuation of the lower end of said condenser tube, and insulating means surrounding said jet adapted to substantially prevent transfer of heat from the jet to the bulb and a conduit communicating with the receptacle to be exhausted and the said bulb and separate metallic projections adapted for air-cooling attached in heat exchange relation to the condensing tube, to the bulb and to the conduit respectively.

Signed at Rochester, New York, this 13th day of February, 1929.

KENNETH C. D. HICKMAN. 

